1. Field of the Invention
The present invention relates to a legged moving robot, and more particularly to an apparatus for detecting the landing position of a foot sole of a legged moving robot at the time the foot sole touches or leaves a floor when the legged moving robot moves up or down a stair or the like.
2. Description of the Prior Art
When legged moving robots such as two-legged walking robots move up or down a stair or on a rough surface, it is desirable to detect the landing position of foot soles of movable legs, i.e., the position of a region of a foot sole which contacts a floor, for enabling the robots to move stably. In particular, it is desirable to detect the landing position of a foot sole when the foot sole touches or leaves a floor.
Specifically, when a two-legged walking robot ascends along a stair with a certain gait (a walking pattern such as a stride), if the landing position of the foot sole of one movable leg at the time the movable leg touches a stair step is too close to the toe, then the other movable leg may possibly miss an upper stair step with the present gait when the other movable leg attempts to reach the upper stair step. Therefore, it is necessary to correct the gait of the robot, e.g., increase the stride, if the landing position is too close to the toe. Similarly, when the two-legged walking robot descends along a stair with a certain gait, if the landing position of the foot sole of one movable leg at the time the movable leg touches a stair step is too close to the heel, then the other movable leg may possibly miss a lower stair step with the present gait when the other movable leg attempts to reach the lower stair step. Therefore, it is also necessary to correct the gait of the robot, e.g., reduce the stride, if the landing position is too close to the heel.
It is thus desirable to detect the landing position of a foot sole when the foot sole touches or leaves a floor in order to correct the gait of the robot.
Prior arrangements for detecting the landing position of a foot sole when the robot moves are disclosed in Japanese laid-open patent publication No. 3-184781 (U.S. Pat. No. 5,255,753) and Japanese laid-open patent publication No. 7-205085 (U.S. patent application Ser. No. 08/363,497).
According to the disclosure of Japanese laid-open patent publication No. 3-184781 (U.S. Pat. No. 5,255,753), as shown in FIGS. 22 through 25 thereof, a matrix of contact sensors are mounted on the foot sole of a movable leg, and output signals from the sensors are processed to recognize a distribution of loads imposed on the foot sole for thereby detecting the landing position of the foot sole.
Japanese laid-open patent publication No. 7-205085 (U.S. patent application Ser. No. 08/363,497) reveals reflective light sensors disposed on respective opposite sides of a robot foot. Based on output signals from the light sensors, the edge of a stair step which contacts the foot sole is recognized to detect the landing position of the foot sole with respect to the stair step.
With the former prior art, since the contact sensors are mounted on the foot sole, the contact sensors are liable to be damaged due to impacts acting on the foot sole when the foot sole touches a floor during movement of the robot. If the contact sensors are covered with an elastic material such as rubber for protection against damage, then the contact sensors are unable to accurately detect a distribution of loads applied to the foot sole. Furthermore, since many contact sensors are employed, a lot of processing operation is needed to process the output signals from the contact sensors.
The light sensors according to the latter prior art are less likely to be damaged or broken. However, in order to prevent the light sensors from being affected by stains on a floor or stair steps, reflecting tapes (markers) need to be applied the floor or the stair steps, resulting in an increase in the cost of the robot. Even if reflecting tapes are employed, the light sensors may accurately detect the reflecting tapes when they are stained.